Documentation

Overview

The TCA9548A is an 8-channel bidirectional I2C switch from Texas Instruments that lets a single microcontroller talk to up to 8 I2C devices that share the same address. If you have ever tried to wire two BME280 sensors to the same bus and watched them collide at 0x76, this is the chip that solves that problem cleanly without bit-banging a second software I2C bus.

The way it works is simple. The master MCU connects to the upstream SDA/SCL pins and addresses the TCA9548A itself at 0x70 (default). You write a single control byte where each bit enables one of the 8 downstream channels (SD0/SC0 through SD7/SC7). Whichever channels you enable get electrically connected to the upstream bus, and the others are isolated. Read your sensor, switch channels, read the next sensor, and so on.

Beyond duplicate-address fanout, the TCA9548A is also handy for mixed-voltage I2C (each child channel is independently level-translated against VCC), for isolating noisy devices from clean sensors, and for building hot-swappable I2C trees. The three address pins A0/A1/A2 let you put up to 8 muxes on the same parent bus, giving you a theoretical 64 child channels from a single MCU. That is a lot of BME280s.

At a Glance

Specifications

Pinout Diagram

Wiring Guide

Code Examples

Arduino — Channel select helper and scan all 8 channels:

#include <Wire.h>

#define TCA_ADDR 0x70

void tcaSelect(uint8_t ch) {
  if (ch > 7) return;
  Wire.beginTransmission(TCA_ADDR);
  Wire.write(1 << ch);
  Wire.endTransmission();
}

void setup() {
  Serial.begin(115200);
  Wire.begin();
  delay(100);

  for (uint8_t ch = 0; ch < 8; ch++) {
    tcaSelect(ch);
    Serial.print("Channel "); Serial.print(ch); Serial.println(":");
    for (uint8_t addr = 1; addr < 127; addr++) {
      if (addr == TCA_ADDR) continue;
      Wire.beginTransmission(addr);
      if (Wire.endTransmission() == 0) {
        Serial.print("  Found 0x"); Serial.println(addr, HEX);
      }
    }
  }
}

void loop() {}

ESP32 — Two BME280 sensors at the same address on different channels:

#include <Wire.h>
#include <Adafruit_BME280.h>

#define TCA_ADDR 0x70
Adafruit_BME280 bme;

void tcaSelect(uint8_t ch) {
  Wire.beginTransmission(TCA_ADDR);
  Wire.write(1 << ch);
  Wire.endTransmission();
}

void setup() {
  Serial.begin(115200);
  Wire.begin(21, 22);

  tcaSelect(0);
  if (!bme.begin(0x76)) Serial.println("BME on ch0 not found");

  tcaSelect(1);
  if (!bme.begin(0x76)) Serial.println("BME on ch1 not found");
}

void loop() {
  tcaSelect(0);
  Serial.printf("Ch0: %.2f C\n", bme.readTemperature());
  tcaSelect(1);
  Serial.printf("Ch1: %.2f C\n", bme.readTemperature());
  delay(1000);
}

Raspberry Pi (Python, smbus2):

from smbus2 import SMBus
import time

TCA_ADDR = 0x70
BUS = 1

def tca_select(bus, channel):
    if channel > 7: return
    bus.write_byte(TCA_ADDR, 1 << channel)

with SMBus(BUS) as bus:
    for ch in range(8):
        tca_select(bus, ch)
        time.sleep(0.05)
        print(f"Channel {ch}:")
        for addr in range(0x03, 0x78):
            if addr == TCA_ADDR:
                continue
            try:
                bus.read_byte(addr)
                print(f"  Found 0x{addr:02X}")
            except OSError:
                pass

Raspberry Pi Pico (MicroPython):

from machine import Pin, I2C
import time

i2c = I2C(0, sda=Pin(4), scl=Pin(5), freq=400000)
TCA_ADDR = 0x70

def tca_select(channel):
    if 0 <= channel <= 7:
        i2c.writeto(TCA_ADDR, bytes([1 << channel]))

for ch in range(8):
    tca_select(ch)
    time.sleep_ms(50)
    devs = i2c.scan()
    print(f"Channel {ch}: {[hex(d) for d in devs if d != TCA_ADDR]}")

Frequently Asked Questions